The expansion of some waxes when they change from a solid to a fluid state when heated is known, and this property has been utilized to provide mechanical power to various mechanisms. When the wax cools sufficiently, it reverts to its solid state and its volume shrinks. It is evident that to keep a system in its actuated condition without additional devices such as retention latches, the wax must be kept hot, because reverse movement would result if the wax were permitted to cool. This is unacceptable for installations where available power is limited such as in spacecraft, and for this reason the use of these actuators has been limited to one-shot installations wherein the actuator's cooling is immaterial to subsequent system operation--it shrinks away from its actuated position, and the powered element generally remains locked in place without provision for its release and return.
But what if reversible and intermittent operation is desired instead? A second heating of hot wax simply would cause the hot wax to resume its previous expanded state, and nothing would be accomplished. No cycling operation would have occurred. The use of a second actuator to provide for a reverse movement is prohibitively expensive, and would add undesirable weight.
It is an object of this invention to provide a hot wax energized actuator which is capable of moving a mechanism to an actuated condition and leaving it there or nearly there after the wax has cooled and solidified, but thereafter, on a second heating of the wax, capable of enabling the mechanism to return to its original condition. Thus, two successive heatings of the wax can cause a mechanism to assume a first actuated (deployed) condition, and then a second unactuated (stowed) condition. Examples of such conditions are a hinged movement in opposite directions from a stowed to a deployed condition, and return.
The utility of a hot wax actuator for actuation purposes is thus extended to enable bi-directional operation with a single intermittently operated actuator, which can importantly reduce cost and weight by requiring only one individual hot wax element for many actuations, and to permit a mechanism to be retracted as well as deployed as the consequence of the expansion and contraction of the wax in a single hot wax actuator.